1. Field of the Invention
The present invention relates to an aqueous dispersion for chemical mechanical polishing, i.e. a polishing slurry for chemical mechanical polishing, and particularly to an aqueous dispersion for chemical. mechanical polishing that is used in a production process of semiconductor devices, resistive to putrefy, scarcely causes scratches and able to form a sufficiently planarized polished surface. The present invention can be utilized in production of semiconductor devices and is useful in, particularly, a micro isolating step and planarizing step of an inter layer dielectric.
2. Description of the Background Art
With the increase of the degree of integration and the formation of multi-layer wiring in semiconductor devices, a memory capacity of memory devices is increasing by leaps and bounds. This is supported by the advancement of micronization of a processing technique. However, a chip size is enlarged in spite of the formation of multi-layer wiring, and the number of steps is increased with the micronization to incur an increase in chip cost. Under the circumstances, a technique of chemical mechanical polishing is introduced for polishing of a film to be processed or the like in the production of a semiconductor device and attracts attention. A great number of micronized techniques such as planarization are embodied by applying this chemical mechanical polishing technique.
As this micronized technique, is known, for example, micro isolation, such as STI (shallow trench isolation) technique (Japanese Patent Application Laid-Open No. 22970/1996 and the like). Various kinds of aqueous dispersions (herein after may be referred to as xe2x80x9cpolishing slurriesxe2x80x9d or xe2x80x9cpolishing slurryxe2x80x9d) for chemical mechanical polishing are used in this micronized technique. In recent years, organic additives have been often contained or incorporated in the polishing slurries for the purpose of improving the polishing performance thereof, and so the polishing slurries are susceptible to be putrefied. Thus, a countermeasure such as to make a polishing slurry strongly acidic or strongly alkaline, or to contain a component for inhibiting putrefaction into the polishing slurry has been taken. For example, hydrogen peroxide or the like is used as the component for inhibiting putrefaction. Further, in the technique described in Japanese Patent Application Laid-Open No. 197575/1991, tetraalkylammonium chloride, tetraalkylammonium hydroxide or the like is contained as a biocide into colloidal silica.
However, a polishing slurry for chemical mechanical polishing containing ceria particles used in the STI technique in particular is generally used in a neutral range, and so there is a limitation to the inhibition of putrefaction by control of pH. The use of hydrogen peroxide fails to retain the action and effect thereof as a preservative over a long period of time, so that putrefaction may progress in the interior of an polish slurry feeding device at a position used in some cases. The other preservatives heretofore used, such as tetraalkylammonium chloride cause scratches and can not prevent dishing although they have anti-putrefaction effect, therefore, they are poor in performance balance.
The present invention has been made for the purpose of solving the above-described problems involved in the prior art and has as its object the provision of an aqueous dispersion for chemical mechanical polishing which does not putrefy even in a neutral range, scarcely causes scratches upon use and able to form a sufficiently planarized polished surface.
According to the present invention, there is provided an aqueous dispersion for chemical mechanical polishing comprising ceria particles, a preservative composed of a compound having a heterocyclic structure containing a nitrogen atom and a sulfur atom in the ring and another, organic component than the preservative, contained in an aqueous medium, wherein the ceria particles, preservative and organic component are contained in proportions of 0.1 to 20% by mass, 0.001 to 0.2% by mass and 0.1 to 30% by mass, respectively, when the total proportion of the aqueous medium, ceria particles, preservative and organic component is 100% by mass.
In the above aqueous dispersion, the ceria particles may preferably have an average particle diameter of 0.01 to 3 xcexcm.
The preservative may preferably be an isothiazolone compound.
The organic component may preferably be at least one of organic abrasive grains composed of resin particles, a water-soluble polymer having a molecular weight of at least 100, an organic acid or a salt thereof and a surfactant.
The aqueous dispersion for chemical mechanical polishing may preferably have a pH of 4 to 10.
The aqueous dispersion for chemical mechanical polishing may preferably be used in dilution at a dilution rate of at least 2 times with the aqueous medium upon use.
The aqueous dispersion for chemical mechanical polishing may preferably be used in a micro isolating step or a planarizing step of an inter layer dielectric in production of semiconductor devices.